Polyether bis-phosphonic acid compounds

ABSTRACT

Polyether bis-phosphonic acid compounds are disclosed which have the formula (HO) 2  OP--R--(OR&#39;) n  --OR--PO(OH) 2  where R is selected from the group consisting of methylene and ethylene, R&#39; is selected from the group consisting of ethylene and ethylene substituted with one or more methyl groups, and n is an integer from 1 to 4, water soluble salts thereof, and esters thereof with alkyl groups having from 1 to 6 carbon atoms. Also disclosed is a novel preparation of certain of these compounds by reacting certain hydroxyalkylphosphonic acid dialkyl ester compounds with certain 2-benzyloxyalkyl organic sulfonates; reacting the intermediate formed therefrom with hydrogen or a hydrogen source; reacting the intermediate formed therefrom with a hydrogen ion acceptor and certain sulfonyl chlorides; and reacting the intermediate formed therefrom with certain hydroxyalkyl-phosphonic acid dialkyl ester compounds to form a polyether bis-phosphonic acid compound which may be hydrolyzed to form the polyether bis-phosphonic acid. Useful intermediates are disclosed which have the formulas ##STR1## HOR&#39;--OR--PO(OR&#34;) 2 , HOR&#39;--OR--PO(OH) 2 , and X--O 2  S--OR&#39;--OR--PO(OR&#34;) 2 , wherein the above-indicated benzene rings of said formulas are optionally substituted with selected groups, wherein R and R&#39; are as defined above, wherein R&#34; is an alkyl group having from 1 to 6 carbon atoms, and wherein X is selected from ##STR2## and alkyl groups having from about 1 to 6 carbon atoms.

FIELD OF THE INVENTION

This invention relates to a novel class of phosphonic acid compoundsuseful in water treatment and to the preparation of those compounds, andmore particularly to a class of polyether bis-phosphonic acid compounds,certain of their precursors and certain derivatives of those precursors,as well as to the preparation thereof from dialkylhydroxyalkylphosphonic acid esters.

BACKGROUND

Much recent research has concerned development of organic corrosioninhibitors which can reduce reliance on the traditional inorganicinhibitors. Among the organic inhibitors successfully employed arenumerous organic phosphonates. These compounds may generally be usedwithout detrimental interference from other conventional water treatmentadditives. Hydroxymethylphosphonic acid has been reported as useful incombination with zinc for corrosion control.

Phosphonic acid compounds have also been used in other fields for suchpurposes as flame retardants, plasticizers, lubricants, and surfactants.U.S. Pat. No. 3,032,578 discloses for example certainaryloxypolyaklylene ether phosphonates which exhibit useful propertiesas surface active agents, and are prepared by reacting a trialkylphosphite with an aryloxypolyalkylene ether halide to form thecorresponding dialkyl phosphonate, which is then hydrolyzed to thecorresponding phosphonic acid.

SUMMARY OF THE INVENTION

This invention relates to a novel class of polyether bis-phosphonic acidcompounds, certain of their precursors, and certain derivatives of thoseprecursors. We have found that certain bis-phosphonic acid compounds maybe prepared by a method which comprises the steps of (a) reacting (i) ahydroxyalkylphosphonic acid dialkyl ester compound of the formulaMOR--PO(OR")₂ where R is methylene or ethylene, R" is an alkyl grouphaving from 1 to 6 carbons, and M is an alkali metal or an alkalineearth metal, with (ii) a compound selected from the group consisting of2-benzyloxyalkyl p-toluenesulfonate, 2-benzyloxyalkyl benzenesulfonateand 2-benzyloxyalkyl alkylsulfonate to form a first intermediate, thealkyl group of said alkylsulfonate having from about 1 to 6 carbonatoms, the oxyalkyl group of said sulfonate corresponding to the formulaOR' where R' is selected from the group consisting of --CH₂ CH₂ --, and--CH₂ CH₂ -- which is substituted with one or more methyl groups, andthe benzene ring of the benzyl group of said sulfonate being optionallysubstituted with one or more substituents selected from the groupconsisting of halogen groups, alkyl groups having from 1 to 30 carbonatoms and alkoxy groups having from about 1 to 30 carbon atoms; (b)reacting said first intermediate with hydrogen or a hydrogen source toform a second intermediate; (c) reacting said second intermediate with ahydrogen ion acceptor and a compound selected from the group consistingof toluene sulfonyl chloride, benzene sulfonyl chloride, and alkanesulfonyl chlorides having from 1 to about 6 carbon atoms to form a thirdintermediate; and (d) reacting said third intermediate with ahydroxyalkylphosphonic acid dialkyl ester compound of the formulaMOR--PO(OR")₂, where R, R" and M are as recited above. The reactionproduct of step (d) may then be hydrolyzed to form a polyetherbis-phosphonic acid. These and other novel polyether bis-phosphonic acidcompounds of the formula

    (HO).sub.2 OP--R--(OR').sub.n --OR--PO(OH.sub.2)

where R is selected from the group consisting of --CH₂ -- and --CH₂ CH₂--, R' is selected from the group consisting of --CH₂ CH₂ --, and --CH₂CH₂ -- which is substituted with one or more methyl groups, and n is aninteger from 1 to 4, as well as water soluble salts thereof and estersthereof with alkyl groups having from 1 to 6 carbon atoms are providedin accordance with this invention. Certain precursors of thesebis-phosphonic acid compounds, and derivatives of those precursors, arealso provided in accordance with this invention especially thosecorresponding to the formulas ##STR3## HOR'--OR--PO(OR")₂,HOR'--OR--PO(OH)₂, and their water salts, where R, R', and R" are asrecited above and the benzene rings are optionally substituted with oneor more substituents selected from the group consisting of halogengroups, alkyl groups having from about 1 to 30 carbon atoms, and alkoxygroups having from about 1 to 30 carbon atoms; as well as thosecorresponding to the formula X--O₂ S--OR'--OR--PO(OR")₂ where R, R' andR" are as recited above and X is selected from the group consisting of##STR4## and alkyl groups having from about 1 to 6 carbon atoms.

It is an object of this invention to provide new and useful phosphonicacid compounds.

It is another object of this invention to provide a novel method ofpreparing certain of these compounds.

These and other objects of this invention will become apparent from thedetailed description which follows.

DETAILED DESCRIPTION

This invention relates to novel polyether bis-phosphonic acid compoundshaving the general formula ##STR5## where R is selected from the groupconsisting of methylene (i.e. --CH₂ --) and ethylene (i.e. --CH₂ CH₂--), R' is selected from the group consisting of ethylene, and ethylenesubstituted with one or more methyl groups (e.g. --CH₂ C(CH₃)H--), and nis an integer from 1 to 4, water soluble salts thereof, and estersthereof with alkyl groups having from 1 to 6 carbons. A preferred groupof these compounds for water treatment includes the polyetherbis-phosphonic acids and their water soluble salts. Alkali metal saltsof these compounds are considered particularly useful for corrosioncontrol applications.

The polyether bis-phosphonic acid compounds of this invention can beprepared from the hydroxymethylphosphonic acid dialkyl ester salts andhydroxyethylphosphonic acid dialkyl ester salts having the formula:##STR6## where R is as described above, R" is an alkyl group having from1 to 6 carbons, preferably methyl or ethyl, and M is an alkali metal oran alkaline earth metal, preferably sodium or potassium.

A method of preparing the polyether bis-phosphonic acid compounds ofthis invention where n is equal to 1 includes the steps of: (a) reacting(i) the hydroxyalkylphosphonic acid dialkyl ester compound of theabove-referenced formula with (ii) 2-benzyloxyalkyl p-toluenesulfonateto form a first intermediate, the oxyalkyl group of saidtoluenesulfonate corresponding to the formula OR' where R' is asdescribed above for the polyether bis-phosphonic acid compounds of thisinvention; (b) reacting said first intermediate with hydrogen or ahydrogen source such as cyclohexene in the presence of palladium oncarbon to form a second intermediate; (c) reacting said secondintermediate with toluene sulfonyl chloride and a suitable hydrogen ionacceptor such as pyridine, substituted pyridines or trialkyl amines toform a third intermediate; and (d) reacting said third intermediate witha hydroxyalkylphosphonic acid dialkyl ester compound of theabove-referenced formula to form tetraalkyl alkyleneglycoldi-(phosphonoalkyl) ether. The reaction product of step (d) (i.e. thetetraalkyl alkyleneglycol di-(phosphono-alkyl) ether) may then behydrolyzed to yield the corresponding alkyleneglycol di-(phosphonoalkyl)ether.

The hydroxyalkylphosphonic acid dialkyl ester salts of theabove-referenced formula may be produced from the correspondinghydroxyalkylphosphonic acid dialkyl ester during preparation. Thus, step(a) is suitably accomplished by adding a solution of thetoluenesulfonate and either hydroxymethylphosphonic acid dialkyl esteror hydroxyethylphosphonic acid dialkyl ester, as appropriate, in asolvent such as ethylene glycol dimethyl ether to a slurry of sodiumhydride in said solvent under an inert atmosphere such as nitrogen orargon. Step (b) is suitably accomplished by dissolving the firstintermediate together with cyclohexene a solvent such as ethanol; addingpalladium on carbon to the solution and heating the resulting slurryunder an inert atmosphere such as nitrogen or argon to reflux. Step (c)is suitably accomplished by dissolving the second intermediate in asolvent such as dichloromethane under an inert atmosphere such asnitrogen or argon; adding toluene sulfonyl chloride to the solution, andadding a solution of pyridine in said solvent to the mixture. Step (d)is suitably accomplished by dissolving the third intermediate togetherwith either hydroxymethylphosphonic acid dialkyl ester orhydroxyethylphosphonic acid dialkyl ester, as appropriate, in a solventsuch as ethylene glycol dimethyl ether and adding the solution to aslurry of sodium hydride in said solvent under an inert atmosphere suchas nitrogen or argon. The alkylene glycol di-(phosphonoalkyl) ether maybe produced by dissolving the tetraalkyl alkyleneglycoldi-(phosphonoalkyl) ether in a concentrated acid, such as hydrochloricacid and refluxing the acid solution.

Accordingly, the compound ##STR7## (i.e., each R is methylene, R' isethylene, and n is 1) may be conveniently prepared by: (a) adding asolution of (i) the diethyl ester of hydroxymethylphosphonic acid and(ii) 2-benzyloxyethyl p-toluene sulfonate in ethylene glycol dimethylether to a slurry of sodium hydride in ethylene glycol dimethyl etherunder a nitrogen atmosphere, thereby forming diethyl2-(benzyloxy)ethoxymethylphosphonate as a first intermediate; (b) (i)dissolving the first intermediate together with cyclohexene in ethanol;and (ii) adding paladium on carbon to the solution of step (b)(i) andheating the resulting slurry under nitrogen to reflux, thereby formingdiethyl 2-hydroxyethoxymethylphosphonate as a second intermediate; (c)(i) dissolving said second intermediate in dichloromethane under anitrogen atmosphere; (ii) adding toluene sulfonyl chloride to thesolution of step (c) (i); and (iii) adding a solution of pyridine indichloromethane to the mixture of step (c) (ii) thereby forming diethyl2-(phosphonomethoxy)ethyl p-toluene sulfonate as a third intermediate;(d) (i) dissolving said third intermediate together with the diethylester of hydroxymethylphosphonic acid in ethylene glycol dimethyl ether;and (ii) adding the solution of step (d) (i) to a slurry of sodiumhydride in ethylene glycol dimethyl ether under a nitrogen atmosphere,thereby forming tetraethyl ethyleneglycol di-(phosphonomethyl) ether.The tetraethyl ethyleneglycol di-(phosphonomethyl) ether may bedisssolved in concentrated hydrochloric acid and the resulting solutionrefluxed to yield ethylene-glycol di-(phosphonomethyl) ether.

We prefer to substantially purify the first intermediate produced instep (a) before proceeding to step (b). This may generally beaccomplished for example by silica gel chomatography. The firstintermediate as described above comprises compounds corresponding to theformula: ##STR8## Moreover, it is considered that the benzene ring ofthe 2-benzyloxyalkyl compound used in step (a) above can be optionallysubstituted with one or more substituents selected from the groupconsisting of halogen groups, alkyl groups, and alkoxy groups, saidalkyl and alkoxy groups having from 1 to about 30 carbon atoms.Accordingly the benzene ring of the first intermediate may becorrespondingly substituted. In addition to their utility in theproduction of the polyether bis-phosphonic acid compounds of thisinvention, these first intermediate esters can themselves be hydrolyzedby conventional means to the corresponding phosphonic acids and watersoluble salts thereof, which are considered useful in water treatment(e.g. as corrosion or scale inhibitors) and, especially for embodimentswhere the benzene is substituted with the longer chain substituents,surfactants.

We prefer to isolate the second intermediate produced in step (b) beforeproceeding to step (c). This may generally be accomplished for exampleby removing the catalyst by filtration and concentrating the filteredsolution under vacuum.. The second intermediate as described abovecomprises compounds corresponding to the formula: ##STR9## In additionto their utility in the production of the polyether bis-phosphonic acidcompounds of this invention, these second intermediate esters canthemselves be hydrolyzed by conventional means to the correspondingphosphonic acids, and water soluble salts thereof, which are considereduseful in water treatment as corrosion and/or scale inhibitors.

We prefer to substantially purify the third intermediate produced instep (c). This may generally be accomplished for example by silica gelchromatography. The third intermediate as described above comprisescompounds corresponding to the formula: ##STR10## Moreover it isconsidered that the toluene sulfonyl chloride used in step (c) above canbe replaced with other reactants such as alkane sulfonyl chlorideshaving from about 1 to 6 carbon atoms, and benzene sulfonyl chloride.Accordingly the third intermediate may be more generally represented bythe formula: ##STR11## wherein X is selected from the group consistingof ##STR12## and alkyl groups having from about 1 to 6 carbon atoms. Inaddition to their utility in the production of the polyetherbis-phosphonic acid compounds of this invention, these thirdintermediate esters can themselves be hydrolyzed to phosphonic acids andwater soluble salts thereof which are considered useful in watertreatment as corrosion and/or scale inhibitors. It is noted that thesulfonate group (whether toluene sulfonate, benzene sulfonate, or alkylsulfonate) may also be removed during such hydrolysis.

The tetraalkyl alkyleneglycol di-(phosphonoalkyl) ether produced in step(d) may generally be purified by dilution with diethyl ether, filtrationthrough celite, and concentration under vacuum. The esters themselvesare considered useful as flame retardants. However, we prefer to usethis purified material for production of the corresponding polyetherbis-phosphonic acids and their water soluble salts, which are corrosioninhibiting agents. The ethyleneglycol di-(phosphonomethyl) ether maygenerally be purified, if desired, by ion exchange chromatography.

The 2-benzyloxyalkyl p-toluenesulfonate used in step (a) may be preparedby conventional techniques from commercially available material. Forexample, a solution of 2-benzyloxyethanol and toluene sulfonyl chloridemay be added to a slurry of sodium hydride in ethylene glycol dimethylether cooled (e.g. using an ice bath) under a nitrogen atmosphere. Afterthe addition, the mixture is warmed and allowed to react at roomtemperature. Crude 2-benzyloxyethyl p-toluenesulfonate may be obtainedfrom the reaction mixture by diluting the mixture with diethyl ether,filtering the diluted mixture through anhydrous magnesium sulfate, andconcentrating the filtered product under vacuum.

An alternative method of preparing the 2-benzyloxyalkylp-toluenesulfonate involves adding pyridine or triethylamine to a cooledsolution of 2-benzyloxyethanol and toluene sulfonyl chloride indichloromethane under a nitrogen atmosphere; warming the mixture andallowing it to react at room temperature; washing the reacted mixturewith dilute hydrochloric acid, sodium bicarbonate solution, and thenwith brine; drying the washed product over anhydrous magnesium sulfate;filtering; and concentrating the filtered product under vacuum.

It is considered that the 2-benzyloxyalkyl p-toluenesulfonate may bereplaced in step (a) by other reactants such as 2-benzyloxyalkylbenzenesulfonate and 2-benzyloxyalkyl alkylsulfonate wherein thealkylsulfonate group has from from about 1 to 6 carbon atoms. Thebenzenesulfonate may be prepared by substituting benzene sulfonylchloride for the toluene sulfonyl chloride in the above syntheses; andthe alkylsulfonate may be prepared by substituting an alkane sulfonylchloride for the toluene sulfonyl chloride. In any case, as suggestedabove, the benzene ring of the 2-benzyloxyalkyl alcohol, may optionallybe substituted with one or more substituents selected from the groupconsisting of halogen groups, alkyl groups having from about 1 to 30carbon atoms, and alkoxy groups having from about 1 to 30 carbon atoms,so that the resultant sulfonate used in step (a) may be correspondinglysubstituted as desired.

A method of preparing the bisphosphonic acid compounds of this inventionwhere n is 2, 3, or 4 involves reacting a hydroxyalkyl phosphonic aciddialkyl ester compound of the above-referenced formula with adihalogenated ether of the formula X--R'--(O--R')_(n-1) --X, where R'and n are as recited above, and X is selected from the group consistingof chlorine, bromine, and iodine, to form the respective tetraalkylester of the bis-phosphonic acid ether. The reaction is suitablyaccomplished by adding a solution of the hydroxyalkyl phosphonic aciddialkyl ester and the dihalogenated ether in a solvent such as ethyleneglycol dimethyl ether to a slurry of sodium hydride in said solventunder an inert atmosphere such as nitrogen or argon. The bis-phosphonicacid ether may be produced by dissolving its tetraalkyl ester in aconcentrated acid such as hydrochloric acid and refluxing the acidsolution.

Accordingly, the compound ##STR13## (i.e., each R is methylene, each R'is ethylene, and n is 2) may be conveniently prepared by adding asolution of the diethyl ester of hydroxymethylphosphonic acid andbis-(2-bromoethyl) ether (i.e. BrCH₂ CH₂ --O--CH₂ CH₂ Br) to a slurry ofsodium hydride in ethylene glycol dimethyl ether under a nitrogenatmosphere, thereby forming tetraethyl bis-(2-phosphonomethoxyethyl)ether. The tetraethyl bis-(2-phosphonomethoxyethyl) ether may bedissolved in concentrated hydrochloric acid and the resulting solutionrefluxed to yield bis-(2-phosphonomethoxyethyl) ether.

The tetraethyl bis-(2-phosphonomethoxyethyl) ether may be purified bydilution with diethyl ether, and filtration through celite, followed bysilica gel chromatography. The esters themselves are considered usefulas flame retardants. We prefer to use this purified material forproduction of the corresponding polyether bis-phosphonic acids and theirwater soluble salts. The bis-(2-phosphonomethyoxyethyl) ether isconcentrated under vacuum to remove hydrochloric acid, and may besubstantially purified, if desired by ion exchange chromatography.However the unpurified product is itself considered useful as acorrosion inhibitor, and typically includes minor amounts of othermaterials such as hydroxymethyl phosphonic acid which is considered notto interfere with the effectiveness of the product and may evencontribute to the product's corrosion inhibiting effectiveness undercertain circumstances.

The triethylene glycol diphosphonomethyl ether compounds (i.e. n=3) andtetraethylene glycol diphosphonomethyl ether (i.e. n=4) compounds may beproduced using basically the same procedure used in producing thebis-(2-phosphono-methoxyethyl) ether compounds, except that thecorresponding dihalogenated ethers are used instead as reactants. Thecorresponding bis-(2-phosphonoethoxyethyl) ether compounds, triethyleneglycol diphosphonoethyl ether compounds, and tetraethylene glycoldiphosphonoethyl ether compounds (i.e. R is ethylene) may be producedusing basically the same procedure used in producing thebis-(2-phosphonomethoxyethyl) ether compounds, except that a dialkylester of hydroxyethylphosphonic acid is used as a reactant instead ofthe diethyl ester of hydroxymethylphosphonic acid, and, as appropriate,the corresponding dihalogenated ethers are employed. It will be evidentthat other polyether bis-phosphonic acid compounds of the inventionwhere n is 2, 3, or 4 may be produced in a similar manner using theappropriate dihalogenated ethers and, the appropriatehydroxyalkylphosphonic acid dialkyl ester reactants.

Salts of the bis-phosphonic acids of this invention may bestraightforwardly produced by neutralizing the acid with the appropriatebase. While esters may be produced as described above, they may also beprepared from the bis-phosphonic acids through conventional phosphonicacid esterification techniques (See, for example D. A. Nicholson et al.,Journal of Organic Chemistry, 35, 3149 (1970).

Practice of the invention will become further apparent from thefollowing non-limiting examples:

EXAMPLE I

To a slurry of sodium hydride (0.4 g,17 mmol) in 20 ml ethylene glycoldimethyl ether cooled with an ice bath under an atmosphere of nitrogen,a solution of 2-benzyloxyethanol (2.1 ml, 15 mmol) and p-toluenesulfonyl chloride (2.9 g, 15 mmol) in ethylene glycol dimethyl ether wasadded dropwise. When the addition was complete, the ice bath was removedand the solution stirred at room temperature for 18 hours. Afterdilution with diethyl ether, the resulting slurry was filtered throughanhydrous magnesium sulfate and concentrated under vacuum to yield 3.6 gof crude 2-benzyloxyethyl p-toluenesulfonate.

EXAMPLE II

Crude 2-benzyloxyethyl p-toluenesulfonate prepared in accordance withthe process of Example I above (3.6 g, 12 mmol) was dissolved in 20 mlethylene glycol dimethyl ether together with diethylhydroxymethylphosphonate (1.65 g, 10 mmol). The resulting solution wasadded dropwise to a slurry of sodium hydride (0.4 g, 17 mmol) in 20 mlethylene glycol dimethyl ether at 0° C. under a nitrogen atmosphere. Thereaction mixture was allowed to warm to room temperature and stirred for3.5 days. The mixture was diluted with diethyl ether, filtered throughmagnesium sulfate and concentrated under vacuum to give 2.5 g of a clearliquid. Purification by silica gel chromatography gave 1.0 g of diethyl2-(benzyloxy)ethoxymethylphosphonate.

EXAMPLE III

Paladium on carbon (10%, 100 mg) was added to a solution of diethyl2-(benzyloxy)ethoxymethylphosphonate prepared in accordance with theprocess of Example II above (0.9 g,2.8 mmol) and cyclohexene (2.0 ml, 20mmol) in 20 ml ethanol under a nitrogen atmosphere. The resulting slurrywas heated to reflux overnight. The catalyst was filtered off and thesolution concentrated under vacuum to yield 0.5 g of diethyl2-hydroxyethoxymethylphosphonate.

EXAMPLE IV

Diethyl 2-hydroxyethoxymethylphosphonate prepared in accordance with theprocess of Example III above (2.5 g, 12 mmol) was dissolved in 13 mldichloromethane under a nitrogen atmosphere. p-Toluenesulfonyl chloride(2.7 g, 14 mmol) was added and a solution of pyridine (2.3 ml, 28 mmol)in 7 ml dichloromethane was added dropwise. After stirring for threedays at room temperature, the mixture was diluted with dichloromethaneand washed successively with water, 1N hydrochloric acid, 5% sodiumbicarbonate and saturated sodium chloride. After drying over anhydrousmagnesium sulfate, the organic phase was concentrated under vacuum toyield 3.3 g of a cloudy liquid. Purification by silica gelchromatography yielded 0.7 g of diethyl 2-(phosphonomethoxy)ethylp-toluene sulfonate.

EXAMPLE V

Diethyl 2-(phosphonomethoxy)ethyl p-toluene sulfonate preapared inaccordance with the process of Example IV above (0.5 g, 1.4 mmol) wasdissolved in 5 ml ethylene glycol dimethyl ether together with diethylhydroxymethylphosphonate (0.3 g, 2 mmol). This solution was addeddropwise to an ice cooled slurry of sodium hydride (0.06 g, 2 mmol) in 5ml ethylene glycol dimethyl ether under a nitrogen atmosphere. Themixture was stirred at room temperature for 25 hours, refluxed for 4.5hours and stirred another 19.5 hours at room temperature. During thisperiod of time an additional 1.0 mmol diethyl hydroxymethylphosphonateand 0.09 g sodium hydride were introduced into the reaction. The mixturewas then diluted with diethyl ether, filtered through celite andconcentrated under vacuum to give 0.3 g of crude tetraethylethyleneglycol di-(phosphonomethyl) ether.

EXAMPLE VI

A solution of the tetraethylethyleneglycol di-(phosphonomethyl) etherprepared in accordance with the process of Example V (1.2 g, 3.3 mmol)in 15 ml concentrated hydrochloric acid was heated to reflux for 3hours. An additional 5 ml of acid was added and the reflux continued foranother 7.5 hours. After standing overnight at room temperature, thesolution was concentrated under vacuum. The residue was dissolved inwater and washed with hexane. Concentration under vacuum gave 0.6 g ofethyleneglycol di-(phosphonomethyl) ether. The structure of theethyleneglycol di-(phosphonomethyl) ether was verified by nuclearmagnetic resonance spectroscopy (carbon-13, proton, and phosphorous) aswell as fast atom bombardment mass spectrometry.

EXAMPLE VII

Sodium hydride (0.24 g, 10 mmol) was slurried in 8 ml ethylene glycoldimethyl ether under a nitrogen atmosphere. The reaction was cooled withan ice bath and a solution of bis-(2-bromoethyl) ether (1.0 g, 4.0 mmol)and diethyl hydroxymethylphosphonate (1.5, 8.0 mmol) in 7 ml ethyleneglycol dimethyl ether was added dropwise. Upon completion of theaddition, the ice bath was removed and the reaction allowed to stir atroom temperature for 3.5 hours. At this point another 0.2 g (1 mmol) ofthe diethyl phosphonate and 0.05 g (2 mmol) of sodium hydride wereadded. After stirring for another 18.5 hours at room temperature, thereaction was diluted with ether and filtered through celite. Thesolution was concentrated and purified on a silica gel column to give0.5 g of tetraethyl bis-(2-phosphonomethoxyethyl) ether.

EXAMPLE VIII

A solution of 4.1 g (10 mmol) of tetraethylbis-(2-phosphonomethoxyethyl) ether prepared in accordance with theprocess of Example VII above in 15 ml concentrated hydrochloric acid(conc. HCl) was heated to reflux for 3.5 hours. Another 15 ml ofconcentrated HCl was added and the solution refluxed another 2.0 hours.After standing overnight at room temperature, the mixture was refluxedan additional 3.0 hours. It was then concentrated under vacuum and driedin a vacuum oven at 80° C. for three days to yield 2.9 g of a viscousoil. Examination by nuclear magnetic resonance spectroscopy (carbon-13,proton, and phosphorous) showed the product to be the desiredbis-(2-phosphonomethoxyethyl) ether, contaminated with 10%hydroxymethylphosphonic acid. The molecular weight of the product wasconfirmed by fast atom bombardment mass spectrometry.

The utility of the polyether bis-phosphonic acid compounds of thisinvention will become further apparent from the following. A standardcorrosive test water solution containing 30 milligrams per liter (mg/l)calcium chloride, 37 mg/l magnesium sulfate, 100 mg/l sodium sulfate, 50mg/l sodium chloride and 100 mg/l sodium carbonate was prepared byadding the recited salts to distilled water. The solution was thus freeof such materials as chromate, zinc, phosphate, polyphosphate, nitrite,nitrate and borate. The test solution was added to a simulated coolingwater test rig having a 12 liter reservoir and a recirculation loop. Therig generally corresponded in design with that described in TheDevelopment and Use of Corrosion Inhibitors, A. Marshall and B. Greaves,Oyez, London (1983). Four precleaned and preweighed mild steel metaltest coupons were immersed in the test solution within the recirculatingloop, and a fifth coupon was immersed in the test solution in thereservoir. The test solution in the rig was maintained at a temperatureof about 55° C., and the pH was adjusted to about 8.5 as the test began.The recirculating flow (generally about 9 liters/min) produced a watervelocity of approximately 1.6 feet/sec. past the coupons in therecirculation line while the water in the reservoir was substantiallyquiescent.

Two of the coupons in the recirculation line were removed after only 24hours, and the remaining coupons were removed after 48 hours. Thecoupons were cleaned after removal and reweighed to determine weightloss. An average corrosion rate in mils (thousandths of an inch) peryear was then calculated for the four recirculation line coupons, and acorrosion rate in mils per year was separately calculated for thereservoir coupon. The corrosion rates for the standard corrosive testwater solution were calculated as 186 mils per year for therecirculation line coupons and 72 mils per year for the reservoircoupon.

A second run (run b) was made using the same procedure except that 15ppm of ethyleneglycol di-(phosphonomethyl) ether (i.e. "EDPME"),prepared generally in accordance with the procedure illustrated above,was added to the standard corrosive test water solution. The corrosionrates for the recirculation line coupons and reservoir coupon werecalculated. The percent corrosion inhibition compared to the run usingonly the standard corrosive test water (run a) is shown in Table A.

Additional runs (runs c, d and e) respectively using EDPME atconcentrations of 22 ppm, 25 ppm and 38 ppm were also made and thepercent corrosion inhibition compared to the run using only the standardcorrosive test water is shown in Table A.

For comparison, hydroxymethylphosphonic acid (i.e. "HMPA") wassynthesized by conventional means from phosphorous acid and formaldehyde(See U.K. Patent Specification No. 1,076,244), and was tested in aseries of 8 runs (runs f through m). The percent corrosion inhibitionusing HMPA at 30 ppm (runs f and g), 50 ppm (run h), 100 ppm (runs i, jand k) and 200 ppm (runs 1 and m) is shown in Table A.

A series of three runs (runs n through p) was made using equal amountsof EDPME and HMPA (10 ppm, 15 ppm and 20 ppm each respectively for thethree runs). The percent corrosion inhibition compared to run a is shownin Table A.

A series of 3 runs (runs q through s) was made using a mixture of HMPAand bis-(2-phosphonomethoxyethyl) ether (i.e. "BPMEE") preparedgenerally in accordance with the procedure illustrated above, as thecorrosion inhibitor. The mixture had a weight ratio of HMPA to BPMEE ofabout 1:9. The percent corrosion inhibitor using a total concentrationof both compounds of 24 ppm (run q), 36 ppm (run r), and 47 ppm (run s)is shown in Table A.

                                      TABLE A                                     __________________________________________________________________________                         Percent Reduction in                                                    Inhibitor                                                                           Corrosion Rate                                           Run Corrosion  Dosage                                                                              Recirculation                                            No. Inhibitor  (ppm) Line     Reservoir                                       __________________________________________________________________________    a   None        0    0 (Base Rate)                                                                          0 (Base Rate)                                   b   EDPME      15    70       35                                              c   EDPME      22    85       19                                              d   EDPME      25    90       32                                              e   EDPME      38    99       98                                              f   HMPA       30    49       43                                              g   HMPA       30    46       41                                              h   HMPA       50    72       26                                              i   HMPA       100   96       56                                              j   HMPA       100   93       37                                              k   HMPA       100   94       43                                              l   HMPA       200   99       62                                              m   HMPA       200   98       75                                              n   EDPME/HMPA(1:1)                                                                          20    66       39                                              o   EDPME/HMPA(1:1)                                                                          30    94       42                                              p   EDPME/HMPA(1:1)                                                                          40    95       44                                              q   BPMEE/HMPA(9:1)                                                                          24    60       22                                              r   BPMEE/HMPA(9:1)                                                                          36    97       17                                              s   BPMEE/HMPA(9:1)                                                                          47    96       71                                              __________________________________________________________________________

The Examples describe particular embodiments of the invention. Otherembodiments will become apparent to those skilled in the art from aconsideration of the specification or practice of the inventiondisclosed herein. It is understood that modifications and variations maybe produced without departing from the spirit and scope of the novelconcepts of this invention. It is further understood that the inventionis not confined to the particular formulations and examples hereinillustrated, but it embraces such modified forms thereof as come withinthe scope of the following claims.

What is claimed is:
 1. A compound of the formula ##STR14## where R is--CH₂ --, R' is selected from the group consisting of --CH₂ CH₂ --, and--CH₂ CH₂ -- which is substituted with one or more methyl groups, and nis an integer from 1 to 4, water soluble salts thereof, and estersthereof with alkyl groups having from 1 to 6 carbon atoms.
 2. A compoundaccording to claim 1 wherein the compound is a polyether bis-phosphonicacid or a water soluble salt thereof.
 3. A compound according to claim 2wherein R' is ethylene.
 4. A compound according to claim 2 wherein nis
 1. 5. A compound according to claim 2 wherein R' is ethylene and nis
 1. 6. A compound according to claim 2 wherein R' is ethylene and n is2.